1. Field of the Invention
The present invention relates to an antenna-embedded laminated glass with an antenna element sealed between glass sheets and a method for preparing the same.
2. Description of the Related Art
Heretofore, an antenna sheet, which comprises a conductive strip for an antenna element and an adhesive layer disposed on a base sheet, has been known (see, e.g., JP-A-2001-119219). This antenna sheet can function as a glass antenna by being bonded to a surface of a glass sheet through the adhesive layer.
Such an antenna sheet is affixed to a surface of a glass sheet in use. From this viewpoint, when such an antenna sheet is bonded to, e.g., an interior surface of the front windshield of a vehicle, the conductive strip needs to be covered with a transparent protective layer. The protective layer is disposed for the purpose of preventing the conductive strip from being damaged and being disconnected by an external force. In some cases, a boundary line between the protective layer and the glass sheet with the antenna sheet affixed thereto is visible since the protective layer has a different refractive index from the glass sheet, and the protective layer covers the glass sheet over a relatively wide area. For these reasons, such an antenna sheet has a problem of poor appearance and a problem of obstructing a driver's view.
On the other hand, in an antenna-embedded laminated glass with an antenna element sealed between glass sheets (see, e.g., JP-A-2-82701), an antenna element is protected by the glass sheets. Even when such an antenna-embedded laminated glass is applied to an automobile windshield, there is no problem, such as a poor appearance caused by the provision of a protective layer in a region except for the provision of the antenna element.
Such an antenna-embedded laminated glass is classified into a print type wherein conductive paste is printed in a desired pattern on an inner surface (mating surface) of a glass sheet to from an antenna element, and an intermediate film embedded type wherein an antenna wire is embedded in an intermediate film (typically made of polyvinyl butyral) interposed between glass sheets.
The above-mentioned print type cannot solve the problems from the viewpoint of a poor appearance or the like since an antenna pattern needs to have a wide line width in order to ensure desired antenna performance because of the presence of large wire resistance.
In this regard, the above-mentioned intermediate film embedded type is advantageous from the viewpoint of poor appearance or the like since an antenna wire having a small diameter can be embedded in an intermediate film.
However, in the case of the above-mentioned intermediate film embedded type, the intermediate film with an antenna wire embedded therein expands or contracts in a heat treatment process, such as press-bonding, to displace the position of the antenna wire in some cases. This is because a laminated glass is produced by sandwiching an intermediate film between two glass sheets, followed by press-bonding and heat treatment. The tendency of such positional displacement causes a problem from the viewpoint of antenna performance. Additionally, there is a problem from the viewpoint of the stability of antenna performance since the tendency of such positional displacement is a major factor in variations in the positions of the antenna patterns of respective final products.